1. Field of Invention
The present invention relates to a polishing apparatus and manufacturing method thereof. More particularly, the present invention relates to a single-layer polishing pad and a method of producing the same.
2. Description of Related Art
During the manufacturing process of semiconductor integrated circuits, isolation structures, metal lines and dielectric layers are stacked layer by layer, and the surface of a wafer is thus less and less planar. Limited by the focus depth of an exposing machine, pattern transferal from a photomask to a photoresist layer is increasingly difficult, and the exposed pattern of the photoresist layer is increasingly distorted. Chemical mechanical polishing (CMP) is the only true global planarization process to resolve the problem mentioned above.
In CMP, a wafer is pressed against on a polishing pad to allow movement of the wafer on the polishing pad having polishing slurry thereon. The polishing slurry contains fine abrasive particles and a chemical reagent. Both the wafer and the polishing pad are rotated automatically; hence the wafer is planarized by mechanical polishing by the abrasive particles and chemical reaction of the chemical reagent.
An important goal of CMP is achieving uniform planarity of the wafer surface, and the uniform planarity also has to be achieved for a series of wafers processed in a batch. The rigidity (or stiffness) and the compressibility (or compliance) of a polishing pad have great influence on the planarity of the polished wafer. Generally speaking, a polishing pad with higher rigidity can increase the polishing planarity of the polished wafer, and a polishing pad with higher compressibility can increase the polishing uniformity of the polished wafer. Therefore, a wafer polished by a rigid polishing pad often needs to be further polished by a soft polishing pad to improve the polishing uniformity. The CMP process thus suffers from low throughput.
Conventionally, to satisfy both the planarity and the uniformity requirements of the CMP process, at least a layer of rigid pad and at least a layer of soft pad are stacked to form a desired composite polishing pad, such as the polishing pads disclosed by U.S. Pat. Nos. 5,212,910 and 5,257,478. As stated in U.S. Pat. No. 6,217,426, although a composite polishing pad can partially satisfy both the planarity and the uniformity requirements of the CMP process, some other problems are also produced. For example, pressure transmission is different for a rigid pad and a soft pad, and the polishing uniformity can sometimes be poor. Furthermore, a greater number of layers stacked in a composite polishing pad creates more variables that can affect the rigidity and compressibility of the composite polishing pad. Hence, the polishing planarity and uniformity are more difficult to control.
Besides, if the two pads in a composite polishing pad are not adhered well enough, the composite polishing pad may easily delaminate during the polishing process. Therefore, U.S. Pat. No. 6,217,426 discloses a polishing pad having a pattern of protrusions on the mounting surface of the polishing pad to limit the pressure transmission area and increase compressibility of the polishing pad.
In the prior art described above, the cost and complexity in producing a polishing pad are unavoidably increased.